At her best, Oprah has promoted reading and self-empowerment, and made generosity glamorous. Photo: WireImage

(
)

Biggest. Impact. Everrrrr!

No single American personality in recent years has influenced our culture as pervasively as Oprah Winfrey, who’s signing off her daytime talk show tomorrow after a 25-year reign of tearful confessions, aha moments, celebrity worship and crazy-expensive free stuff.

Her first name itself has become, for many, a kind of self-help mantra. (“I pretty much just do whatever Oprah tells me to,” says Tina Fey’s character on “30 Rock,” when asked what her religion is.) To appear as a guest on her show was to know you would wake up the next day to a staggeringly different level of fame. To be a member of her live studio audience was to know you would weep at least once.

The “Oprah effect” has shaped our national consciousness in profound ways. “There are a lot of people whose lives are better, thanks to what she’s done,” says Robert Thompson, founding director of the Bleier Center for Television and Popular Culture at Syracuse University. “Her whole message of empowerment is the idea that you can change your circumstances.”

Occasionally, however, that influence has seriously misfired. “Oprah has mainstreamed a lot of very questionable characters in my opinion,” anti-cult therapist Steven Hassan has said, pointing to Oprah acolyte James Arthur Ray whose infamous sweat lodge led to the deaths of three people in 2009.

The megalithic TV host and producer has also arguably helped to foster an unprecedented level of national narcisissm, and a mass susceptibility to snake-oil salesmen disguised as self-improvement gurus. She’s given a national platform to controversial topics, such as the “link” between childhood vaccines and autism, which have had ramifications far beyond the Nielsen ratings.

And, as writer Jennifer Simon pointed out on Nerve.com, “her biggest contribution to the self-improvement landscape is her promotion of retail therapy — the idea that you can spend your way to happiness and fulfillment.”

Her attachment to self-betterment by way of better stuff became a national religion, wherein audiences at her “Favorite Things” episodes went through evangelical seizures when given free high-end appliances, designer clothes, the latest gadgets and, occasionally, cars. Comedian Kathy Griffin, a fervent fan of Winfrey’s show, poked fun at the TV star’s oft-inexplicable choice of gifts: “She’s like, ‘You’re all getting genuine thick woolen Ugg boots!’ In Macon, Ga. Where, today, it is 103 degrees.”

More seriously, the show’s emphasis on the confessional format, in which a guest comes clean about or apologizes for some wrongdoing — as Sarah Ferguson recently did, for selling access to Prince Andrew — became one of its hallmarks, and arguably inspired a nation of copycats.

“She’s really desensitized the public, so it’s OK to screw up royally. It’s OK to be extremely pathological — we’ve seen it all on ‘Oprah!’ “ says Manhattan psychotherapist and advice columnist Jonathan Alpert. “People think that if they get in front of some cameras and admit wrongdoing, that they’re better. [But] whether it’s Arnold [Schwarzenegger] and Maria [Shriver], or any of these countless politicians that have gotten into trouble lately, putting your private life on display doesn’t actually make everything better.”

Winfrey even invented her own confessional language, with moments both “teachable” and “a-ha.” But, as Alpert points out, “life doesn’t work in sound bites. Psychotherapy doesn’t work in sound bites.”

Neither, he says, does it work in the kind of language endorsed in some of Oprah’s favorite self-help tomes, such as Rhonda Byrne’s “The Secret,” a book that teaches that positive thinking can dramatically alter one’s life.

“I think ‘The Secret,’ and all those other things, are absolute garbage and grossly irresponsible — telling people to hang a picture and wish for something,” Alpert says. “Without a strategic plan, they just give people a false sense of hope.”

But Winfrey herself had the audacity to hope for — and successfully help elect — the country’s first black president. A recent economics study by the University of Maryland found Winfrey’s endorsement yielded 1,015,559 votes for Obama.

Whatever you think of his election triumph, Oprah has undoubtedly used her powers for good in other significant arenas. Without her, many Americans would never have entertained the idea of reading for fun. Starting in 1996, Oprahs’s Book Club, a segment on her show, began selecting and promoting books to her readers, resulting in 30 million book sales — a revitalization of the publishing industry with a wave of her magic wand. She even managed to put the Russian classic “Anna Karenina” in the No. 1 spot on USA Today’s best-seller list.

“She was able to convey this idea that you don’t have to be a trained scholar to interact with books,” says Kathleen Rooney, author of “Reading with Oprah: The Book Club that Changed America.”

“She got people talking about them and recommending them to friends. She rejuvenated the phenomenon of the book club as a social gathering place in America.”

’“”“”She has also given millions to charity and, in the process, brought the concept of philanthropy to the masses. Recently, Oprah showcased her favorite guests during the lead-up to her final show. Her ultimate favorite, Tererai Trent, was a success story who’d grown up as an abused child bride in Zimbabwe and made her way to the US to earn a PhD. The episode culminated in a giveaway of a million dollars to build a school in Trent’s home country. “It’s psychologically satisfying to watch people be that generous,” says social psychologist Karen Dill. “I know she’s a cultural icon, and people can certainly make fun of Oprah, but I do think she’s doing genuinely good work by doing those things on the air.”

Winfrey elevated the status of the daytime talk from a trashy, chair-throwing medium like “The Jerry Springer Show” to a place in which taboo subjects were discussed with dignity, gravitas and — always — tears. And her disclosure of her own struggles, such as her early-on story of childhood sexual abuse and her continuing public struggle with eating, helped fuel people’s connection with her. “She has shown us her own vulnerabilities,” says Dill, “and people find that very attractive.”

At the root of her empathy, and the secret to her connection to us, is her own rags-to-riches narrative. From an abused adolescence in a small farming town in Mississippi, she worked her way through school and into television in Tennessee, eventually moving on to her own show in Chicago and the national stage.

“You can’t beat her as a story for overcoming,” says Dill, who blogs about media influence at Psychology Today. “The story of her childhood, of being a black woman at that time in Chicago. Coming up in journalism to become one of the richest people in America. It’s really amazing, what she’s been able to overcome herself.”

“Oprah, for African-Americans, became the person who made America comfortable with a black presence in their living rooms on a daily basis,” Al Sharpton has said of her. “ ‘And she was able to do it in a way that brought us dignity. She didn’t do it as sex object, she didn’t do it as a comedian. She was thoughtful and professional.”

Except, that is, when she was meeting her idols. As good as she is at relating to the average woman, Winfrey has a soft spot for fame, retaining a revolving cast of beloved movie and TV stars who regularly graced her couch — including John Travolta, Julia Roberts, Tom Hanks and Tom Cruise, the last of whom memorably jumped up and down on her couch while declaring his love for future bride Katie Holmes.

“For Oprah, it was always clear that the encounter with celebrity was a religious experience,” wrote Laura Bennett in the New Republic earlier this year.

On Wednesday, as Oprah tunes out for good, millions of Americans will be losing their religion. But a crisis of faith may end up, surprisingly, being their own salvation.